• Paul Mackerras's avatar
    [POWERPC] Fix off-by-one error in setting decrementer on Book E/4xx (v2) · 43875cc0
    Paul Mackerras authored
    The decrementer in Book E and 4xx processors interrupts on the
    transition from 1 to 0, rather than on the 0 to -1 transition as on
    64-bit server and 32-bit "classic" (6xx/7xx/7xxx) processors.  At the
    moment we subtract 1 from the count of how many decrementer ticks are
    required before the next interrupt before putting it into the
    decrementer, which is correct for server/classic processors, but could
    possibly cause the interrupt to happen too early on Book E and 4xx if
    the timebase/decrementer frequency is low.
    
    This fixes the problem by making set_dec subtract 1 from the count for
    server and classic processors, instead of having the callers subtract
    1.  Since set_dec already had a bunch of ifdefs to handle different
    processor types, there is no net increase in ugliness. :)
    
    Note that calling set_dec(0) may not generate an interrupt on some
    processors.  To make sure that decrementer_set_next_event always calls
    set_dec with an interval of at least 1 tick, we set min_delta_ns of
    the decrementer_clockevent to correspond to 2 ticks (2 rather than 1
    to compensate for truncations in the conversions between ticks and
    ns).
    
    This also removes a redundant call to set the decrementer to
    0x7fffffff - it was already set to that earlier in timer_interrupt.
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    43875cc0
time.c 31 KB